This invention relates to shaped charges and to the use of shaped charges in explosive blasting and in particular to the reduction of Nitrogen Oxides from explosive blasting in the mining industry.
The art of shaping a detonation charge to do work is a very well documented process. Explosions used to perforate well casings, heavy armor piercing shells and fireworks are all examples of shaping explosive energy.
In prior art blasting techniques a booster or primer is mainly used to further initiate a less sensitive blasting agent. The boosters usually range from one to five pounds in weight and are available in several compositions and shapes. During blasting a detonator or booster is used to provide a sufficient amount of energy to the blasting agent in order to initiate a sustained reaction in the blasting agent which travels from the point of initiation, usually the bottom of a bore-hole, through the entire column of blasting agent. The dynamics of the reaction in the blasting agent depend on the amount, shape and direction of the energy produced by the detonator or booster.
The direction of the initiation energy has many effects. Ideally the initiation energy produced by the detonator or booster directs the energy upward to the column of blasting agent and does not direct energy downward toward mineral strata. This protects the strata from damage yet accomplishes the initiation of the blasting agent column. In a shape charge booster the energy is also directed upward and not outward radially. If energy is directed radially outward, other bore-holes may be damaged.
The shape of the initiation energy has significant effects on the overall blast as well. The shape of the energy wave produced by the booster or detonator often determines the dynamics of the reaction of the column of blasting agent. As shown in U.S. Pat. No. 4,938,143, the increase in surface area of the contact between the blasting agent column and the booster partially determines whether the blast is overdriven or underdriven. This corresponds to the reaction dynamics and the overall effectiveness of the blast. The ideal reaction of the column of blasting agent is one that reaches hydrodynamic velocity or steady state velocity immediately at the point of initiation. By shaping the initiation energy wave a steady state velocity is reached more quickly and the efficiency or effectiveness of the blast is improved. Additionally, the initial shape of the energy wave produced assists in detonating the entire cross-section of the column of blasting agent. As opposed to a narrow lance of directed energy, by projecting the energy wave to encompass the sides of the blasting agent column the initiation energy initiates the entire cross-section of the column and produces a more desirable reaction traveling up the blasting agent column.
The amount of energy produced by a booster or detonator is also a concern for the efficient and sufficient detonation of the blasting agent column. The amount of energy produced by a booster should be enough to effectively initiate the column of blasting agent, but not so much as to affect the mineral strata, other bore-holes or the reaction of the column of blasting agent. Too much energy from the initiation may produce a blow-out or other effects that do not react the column of blasting agent. By controlling the amount shape and direction of the initiation energy a blast""s efficiency and effectiveness is controlled for the desired results.
Often the conditions present in blasting greatly affect the efficiency of the blast. During blasting operations bore-holes are drilled and set with detonation means, booster means or both and then the blasting agent is supplied into the bore-hole before the detonation of the explosives. In some instances the blasting agent lies in the bore-holes for considerable time before the detonation. Often the blasting agent is adversely affected when allowed to sit for extended periods of time. The adverse effects are most profound near the bottom of the bore-holes where any water or other contaminants collect and the detonation or boosting means is located. The adverse effects seen in bore-holes may be wetting of the blasting agent, breaks or discontinuities in the basting column or other effects. When adverse conditions are present in blasting the use of prior art shaped boosters and detonators does not lead to the desired results that is the efficient initiation of the blasting agent. If the blasting agent surrounding and immediately atop the boosters or shaped charges is adversely affected by conditions present in the bore-hole, the shaped charge or booster directs a shock wave at blasting agent which does not sufficiently propagate the desired shock wave or reaction. The boosters in use may shape the energy wave correctly but the size of the initial detonation is normally not sufficient in order to overcome effects of the conditions present in the bore-holes.
When using blasting as a tool for mining or other industries the bore-holes are sometimes angled, to effectuate a desired use of the energy released during blasting. Often the angled bore-holes adversely affect the results of the blast. Blasting agent may settle to one side of the bore-holes. When using prior art type boosters the orientation of the booster is critical in obtaining efficient use of the explosives. In angled bore-holes the orientation of most prior art boosters are suspect. When a small shaped charge or booster is placed in a bore-hole, the booster or charge aligns with gravity forces and is often directed out of the perpendicular cross-section of the explosives column. While the prior art mentions the critical orientation of the shaped charge in relation to the cross-section of the blasting column it does not mention the means of achieving such orientation of the booster in the bore-holes and in particular the orientation in angled bore-holes.
Shaped charge detonation is a technique known to the mining industry, and almost all of the manufacturers of cast boosters sell a shaped booster for various applications. The art of shaping a charge is thoroughly explained in U.S. Pat. No. 4,938,143. U.S. Pat. No. 4,938,143 provides experimental proof that xe2x80x9csteady state velocityxe2x80x9d is reached as quickly as possible with shaped detonation. Though it is not explained in the patent, molten explosives were poured into a conical shaped mold and then solidified to make the shaped booster. U.S. Pat. No. 5,705,768 takes the invention in U.S. Pat. No. 4,938,143 one-step further by adding a shaped form on top of a cast booster. This invention fills the cylindrical end with inert material rather than explosive. The explosive incorporated into the design is a conical form at the top of the device. The explosive is conical shaped, and the resulting explosion is shaped because it takes the form of the cone through which the energy is broadcast. It also addresses the use of shaped charges to more effectively initiate the blast to remove overburden from mineral strata. In U.S. Pat. No. 5,705,768, the shaped charge directs energy with the use of a concave recess atop the shaped charge whereby the energy wave is broadened outwardly and up through the powder column. However, the arrangement disclosed in U.S. Pat. No. 5,705,768 does not solve orientation problems within bore-holes or address blast initiation of the entire cross section of the powder column to achieve faster steady state or hydrodynamic velocity. Though U.S. Pat. No. 5,705,768 does not have experimental findings it does reference U.S. Pat. No. 4,938,143 as the document to prove the value of the shaped charge. In fact, the technique of shaping a detonation is well known in the art. U.S. Pat. No. 4,938,143 is hereby incorporated by reference to demonstrate that shaped detonation is more efficient.
The present art is specific to casting explosive material in various shapes, the largest of which is 4 pounds. Research has demonstrated that a shaped booster is far more efficient in obtaining hydrodynamic velocity than the commonly used cylindrical booster; however, the shaped booster is not successfully used in cast blasting. The disadvantage of the present art is that a small booster will not be orientated correctly when it reaches the bottom of a bore-hole. If the shaped detonator were upside down it would extremely compound the problem of low detonation velocity and concern about orientation may be the primary reason for not using the existing technology. Although shaped boosters are not being used in cast blasting the low profile boosters are. These flat boosters are being used like a shaped charge booster because they have a large surface area in contact with the Ammonium Nitrate blasting agent. This large area spreads the energy across the face of the powder column, just as the shaped charge would do, but there is no fear of incorrect orientation with this type of symmetrical booster.
According to the prior art, shaped boosters of many designs address the need for attaining a steady state velocity of the explosive wave front within inches of the booster. Additionally, some of the prior art addresses the need for shaping the wave front produced by the booster in order to obtain a more efficient blast. However, the prior art does not address the initiation of the entire cross-section of the explosives column with sufficient energy to overcome adverse conditions.
In addressing the efficiency, effectiveness and sufficiency of a blast, a specific problem with blasting is also addressed. In many blasts the production of pollutants is of great concern. The pollutants are a direct result of an improper reaction occurring during detonation. Particular blasting agents have a tendency to produce environmental pollutants during and after a blast is initiated. In particular, ANFO produces orange clouds of Nitrogen Dioxide. Although much of the description is directed toward the production of pollutants from an Ammonium Nitrate Fuel Oil (ANFO) blast, the illustration of the reaction is equally applicable to other types of explosives and their consequent improper detonation reactions. Similarly, the use of explosives is emphasized by way of example for the mining industry and in particular the coal mining industry. However, the discussion and invention are applicable to other uses of explosives and any limitation contained herein is for illustration purposes.
The surface mining industry has long been plagued by the formation of toxic Nitrogen Dioxide from Ammonium Nitrate and fuel oil blasts, but more so with the now common technique of Cast Blasting. The Cast Blast pattern is set up to throw the overburden (dirt) off of the coal seam, which allows the mine to produce more tons of coal at a reasonable cost. The: problem with Cast Blasting is that the ANFO columns are 100 feet deep and the blasting agent must be put into the bore-hole days before the blast. The longer the ANFO is in the bore hole the greater the chance the blasting agent immediately around the detonator is affected by temperature, pressure and water. If the blasting agent integrity is compromised around the detonator, the blasting agent does not ignite with sufficient energy and noxious Nitrogen Dioxide gases are formed. The Nitrogen Dioxide is very visible as large clouds of orange smoke.
Clouds of Nitrogen Dioxide gas have become common and severe since the cast blasting technique was introduced. Although changes in blasting schemes have helped reduce the Nitrogen Dioxide, the pollutant still has not been eliminated and the mining industry""s profitability is being affected.
Deflagration and the subsequent Nitrogen Dioxide (NO2) formation is not a new problem, but the magnitude of the problem has intensified to become an environmental concern. In 1994, the technique called cast blasting began to be the standard practice for breaking up the overburden to get to coal seams. Not only did the technique make the dirt shoveling easier; it cast 35% of the dirt into the mined out trough so that it did not have to be shoveled at all. However, it is the cast blasting technique that became notorious for producing huge clouds of Nitrogen Dioxide gas with every blast. An estimate of the concentration of Nitrogen Dioxide in a typical xe2x80x9corange cloudxe2x80x9d is about 1,000 pounds and this new source of Nitrogen Dioxide has become a significant environmental concern as well as a public health threat.
The change from load-and-shoot blasting to cast blasting has undoubtedly affected the chemistry of the blast and has lead to the creation of Nitrogen Dioxide clouds. The bore holes are three times deeper, the blasting agent xe2x80x9csleepsxe2x80x9d in the ground for many days, and there is no way of knowing if the detonator is surrounded by active blasting agent at the bottom of these bore holes. It would appear that some basic principle of blasting was violated when cast blasting was introduced to some areas.
The particular type of blasting that has lead to the creation of the Nitrogen Dioxide problem is cast blasting. The blasting technique was investigated to determine the factors that might affect the chemistry. The sequence of a cast blast is disclosed below.
The cast blast is set up to kick the overburden off into the already mined out trough left by the coal seam. The bore holes are drilled at a 20xc2x0 angle to ensure that the toe of the bench slides into the trough. The holes are pushed all the way to the coal seam and then back filled with ten feet of dirt to position the blast just above the coal seam. When the blast is detonated, the front row of holes initiates first. This breaks up the overburden and starts it moving outward and downward toward the trough. Blowing the front row provides relief for the next row so that the new blast wave can broadcast the dirt outward.
When the second row of holes is initiated the second relief of dirt follows the first. The cast blast is designed to be powerful enough to put the first relief of dirt in the trough and put about half the second relief of dirt on top of the first. A good cast blast should move 35% of the overburden off of the coal seam. The loosened rock or muck, blown into the trough, does not have to be shoveled. The first row will blow the hardest because the rock is still tight and the gas energy has a solid wall to push against. As each row blows the ground becomes fractured and fissures allow some of the gas energy to be lost, which limits the amount of cast achieved by the last row of holes. The third row detonation blows into the relief of the second row blast and drops the muck on top of the coal.
The cast blast results in a 45% cast. It is the success of the blasting program that dictates the overburden removal costs. The more dirt that is cast off of the coal seam the less dirt that must be shoveled. The overburden to coal ratio is an important economic number to coal mining, as is the cost per cubic yard to remove overburden. The end result of a cast blast is an orange cloud of Nitrogen Dioxide gas. The poisonous gas rises out of the muck pile for many minutes after a cast blast.
It is therefore an object of at least one aspect of the present invention to address the problems and disadvantages above.
It is an object of the present invention to overcome the adverse conditions often times present in bore-holes and to supply a device which ensures a large amount of dry or unaffected blasting agent for sufficient initiation of the blast.
Another object of the present invention is to provide an effective shaped charge for use in the explosives and mining industry.
Yet another object of the present invention is to address the need to increase detonation power to reach steady state velocity as quickly as possible.
It is an object of the present invention to provide a capsule for the blasting industry that is not an explosive but can be made into a shaped explosive charge by the user or blaster.
It is also an object of the present invention to provide a device that does not require special care to orientate the shaped charge toward the powder column.
Another object of the present invention is to provide a device that can be added on top of the existing system to enhance the detonation of the booster.
Yet another object of the present invention is to provide a device that can slide down an angled bore-hole and orient the shaped charge toward the powder column.
Still another object of the present invention is to provide a device that has enough weight to ensure it reaches the bottom of a bore-hole greater than 100 feet deep.
It is an object of the present invention to provide a device that can be made to have a density greater than water so it can sink through water.
Another object of the present invention is to provide a device to ensure that the blast energy of the detonator contacts 25 pounds of blasting agent that has not been compromised by temperature, pressure and/or water.
Still another object of the present invention is to provide a device that ensures that the blasting agent in intimate contact with the booster does not diffuse into the formation.
Yet another object of the present invention is to provide a device that can be added to the existing system when additional energy is needed.
It is an object of the present invention to provide a device that can be varied to deliver blast energy so the explosion is not overdriven or under driven.
It is an object of the present invention to overcome the adverse conditions often times present in bore-holes and to supply a device which ensures a large amount of dry or unaffected blasting agent for initiation of the blast.
It is yet another object of the present invention to initiate an entire cross section of a blasting agent column to produce a steady state hydrodynamic shock wave at or near the bottom or area of a capsule in order to completely fire the column efficiently.
Another object of the present invention is to provide a device that can be placed at varied points in the bore-hole to accelerate the energy as needed.
Other objects of this invention will become apparent from the following description.
This invention is a shaped charge in the form of a capsule designed to contain high energy blasting agent. The capsule may be filled and shipped as an explosive device or may be shipped as a capsule and filled with explosives at or near the site of blasting by the end user or blaster. The present invention is a tool to augment the existing blasting technology. In the event of shipping the capsule not filled with any explosive materials it does not qualify as a munitions, ordinance, pyrotechnic, bomb and or any other DOT Class 1 material so it may be shipped at a reasonable cost anywhere in the world. The present invention is a shaped charge that utilizes a capsule to sufficiently, efficiently and effectively initiate a column of blasting agent. The filled capsule produces an initiation energy for a detonation of a column of blasting agent. The amount, shape and direction of the initiation energy is controlled by the capsule in order to efficiently and sufficiently react the blasting agent column for an effective blast. The present invention overcomes the conditions common in bore-holes such as contamination and corruption of the blasting agent and column, and the difficulties in the orientation of boosters and other initiators. The present invention also addresses the need for a large quantity of explosives to sufficiently and properly initiate a column of blasting agent. The present invention also reduces the amount of pollutants emitted by cast blasting.
This invention utilizes a capsule which shapes detonation energy to assure hydrodynamic velocity is reached closer to the initial site of detonation of the explosive blasting agent column and to prevent the formation of pollutants in mining blasts. By ensuring the detonation reaches hydrodynamic velocity at or near the initial site of detonation, the capsule increases the efficiency of the blasting agent column to achieve the desired results of the blast. Additionally, focusing the energy of the initial detonation at the blasting agent ensures the powder column reaches hydrodynamic velocity so it does not produce pollutants. The present invention provides a detonation system that can be used to solve the xe2x80x9corange smokexe2x80x9d problem in cast blasting.
This invention is a technical solution to the environmental problem and thus a solution to keeping the mining industry profitable. By initiating ANFO powder columns with concentrated energy, the formation of Nitrogen Dioxide is dramatically reduced. This invention is a plastic capsule that is to be filled with high energy blasting agent and fitted with a standard detonator means. The design of the capsule ensures that a large volume of blasting agent is protected from degradation and further ensures that the hydrodynamic velocity of the detonation is energetic enough to prevent Nitrogen Dioxide formation.
This invention is designed to address two other problems in the detonation of a bore-hole filled with blasting agent. The capsule is designed to protect up to 30 pounds of blasting agent from the affects of temperature, pressure and moisture at the bottom of the bore hole. The capsule further ensures that a commonly used cylindrical cast booster or other detonation means is in intimate contact with a sufficient amount of unadulterated blasting agent that will immediately initiate the powder column at hydrodynamic velocity. The capsule is shaped such that it projects the energy of the detonation directly at the column of blasting agent to spread the supersonic gas jet to the sides of the bore-hole. By providing the assurance that the detonator system will initiate with maximum energy, the Ammonium Nitrate will react completely and not form environmental pollutants. The capsule will protect and project the blast energy to ensure hydrodynamic velocity is obtained at the bottom of the blast hole or at the capsule location.